1. Field of the Invention
This invention relates to a drainage pump, in particular, for use in an air conditioner.
2. Related Art
In an indoor unit of an air conditioner in refrigerating operation, moisture in the air condenses into waterdrops in a heat exchanger and falls into a drain pan located under the heat exchanger. A drainage pump is equipped to discharge water from the drain pan. There are various conventional types of drainage pumps, including one comprising an upper-opened housing having a suction inlet in its bottom wall and a delivery outlet in a side wall, and an impeller accommodated in the housing and rotated by a motor fixed above the opening of the housing via a cover. The axle of the motor rotatably extends through and beyond the cover and is coupled to the axle of the impeller. The cover has a through bore communicating the interior space of the housing with the atmospheric air. When the impeller is driven by the motor, water in the drain pan is drawn by the lower end of the impeller, pumped by the centrifugal force, and discharged through the outlet to the exterior.
The conventional drainage pump involves the problem that noise occurs when drainage of water starts. This is caused by bubbles that are produced from the liquid around the impeller and hit the impeller and interior surfaces of the housing.